Teletypewriter secrecy system



E. w, BEMns ZAMfiSQ TELETYPEWRITER SEOREGY SYSTEM Filed June 27, 1942 2 Sheets-Sheet 1 B '0 Fansmitter adL INVENTOR E WBenus BY W W TTQRNEY- 2 Sheets-Sheet 2 E. W. BEMIS TELETYPEWRITER SECRECY SYSTEM Filed June 27, 1942 FKMIFP INVENTOR E Wflelmw I L7,; ATTORNEY Patented June 4, 1946 UNITE TELETYPEWRITER SECRECY SYSTEM Application June 2'7, 1942, Serial No. 448,736

14 Claims.

This invention relates to telegraph and teletypewriter systems. More particularly, this invention relates to telegraph and teletypewriter system suitable for the secret transmission of signals.

It has heretofore been proposed to transmit telegraph or teletypewriter signals or characters secretly by converting each character to be transmitted into a difierent character according to a predetermined code so that the transmitted character or signal will be different from the character or signal intended to be transmitted. At the receiving station the same predetermined code will be utilized to derive from the transmitted character the original character in its true form. It is essential in such systems to maintain the coding and decoding devices, otherwise known as the enciphering and deciphering devices, respectively, in Synchronism at all times in order that the characters or signals may be reproduced so as to be intelligible.

In utilizing radio or other transmission paths for the transmission of such signals it may happen at times that the transmitted signal becomes faded or otherwise suppressed, in which event the deciphering mechanism may be retarded with respect to the enciphering mechanism and thereafter the subsequent characters and signals will be rendered unintelligible. At other times extraneous voltages or static crashes or the like may be superimposed upon the transmitting medium and enter the apparatus at the receiving point, thereby causing the deciphering mechanism to step ahead of the enciphering mechanism. The reproduced signals or characters will then also be rendered unintelligible thereafter.

According to the present invention it is proposed to provide means at the receiving point to effectively restore intelligibility to the signals after the phase between the enciphering and deciphering devices has been distorted. It is also proposed to employ at the receiving point a reperforator-transmitter in addition to the deciphering equipment, whereby the received signals will be perforated in tape so that they may be stored and re-transmitter through the receiving equipment after the deciphering device has been effectively brought into synchronism with the received signals or characters.

It is a feature of this invention to employ at the receiving point apparatus for advancing or retarding the deciphering equipment step-bystep with respect to the transmitting equipment of the reperforator-transmitter. This apparatus will be used to advance or retard the deciphering 2 equipment by one or more characters until the deciphering equipment is brought into synchronism with the signals or characters being transmitted by the reperforator-transmitter. This will permit the faithful reproduction of substantially all of the characters and signals even during abnormal conditions of transmission, the reproduction being effected after synchronism is restored between the equipments.

It is a further feature of this invention to arrange the apparatus so that after the deciphering equipment is eifectively brought into synchronism with the received signals or characters the perforated tape at the reperforator-transmitter may be returned to the point where the deciphering equipment fell out of step with the transmitter equipment and the signals or characters perforated in the tape then allowed to pass through the apparatus for the faithful reproduction of these characters and signals thereafter.

This invention will be better understood from the more detailed description hereinafter following when read in connection with the accompanying drawings in which Figure 1 illustrates a radio transmitter apparatus including enciphering equipment, and Fig. 2 illustrates a radio receiver for reproducing the characters or signals received from the radio transmitter, the receiver including a reperforator, a transmitter-distributor and deciphering equipment, as well as appa- 1 ratus for advancing or retarding the deciphering equipment to any desired extent with respect to the transmitter-distributor.

Referring to Fig. 1 of the drawings, the reference character .TTYi designates a teletypewriter having the usual transmitting contacts T01 and a magnet MGI which controls a typing unit (not shown) forpreparing local copy of signals or characters to be transmitted. Fig. 1 also shows enciphering equipment EQ including a transmitter-distributor 'I'Di having enciphering contact.

apparatus C01. The enciphering equipment EQ includes a perforated tape prepared in advance (not shown), the tape having a great many .characters perforated therein according to difierent letters and numerals. The tape may or may not be of the endless type so that the same characters in the same order may or may not be used repeatedly as desired. The radio transmitter RT will transmit through the ether a signal or character which is difierent from that typed by the teletypewriter TTYl, the signal or character transmitted being dependent upon the signal or character of the enciphering equipment EQ which is mixed therewith. It will be shown hereinafter that in transmitting, for example, the character J from the teletypewriter TTY1, the radiotransmitter will transmit the letter X when the enciphering equipment EQ is set for the character D.

Assuming that the teletypewriter TTY1 is typing the character J which comprises, in addition to the usual starting and stopping pulses, the five pulses-mark, mark, space, mark and space, the starting pulse will cause the armature of relay R1 to close its spacing contact S. 'The relay R2 will in turn close its spacing contact S. Spacing or positive battery will then beconnected tethe starting magnet SM1 over a circuit which includes the spacing contact S and armature of relay R2, the inner ring RG1 of the transmitter-distributor TD1, the armature ARl, brushes BB1 and BB1,

' rent in this winding falls. to zero gradually during the interval that condenserCi is receiving a substantial charge of current. After the charging current has diminished. sufificiently the relay R4 will move its armature to its spacing contact S. Spacing or positive potential will thereby be applied to the point. PT of a balanced bridge circuit, the applied positive potential then causing a flow of current through the upper or main winding of relay R whereupon the armature of relay R5 will close its spacing contact S. Current in the lower or looking winding of relay R5 holds the armature firmly in. this position. The relay R6 will then follow the relay R5 to transmit'the starting or spacing pulse through the antenna circuit. The modulating apparatus of the radio transmitter is not shown, as it may be of any well-known type. The resistor Z1, included in series with the upper or bias winding of the relay R4, is employed in a well-known manner to control the amount of delay interposed in the transmission of the starting signal to cause it to have the. correct relation. to the other pulses to be transmitted as described. below by the radio transmitter RT.

The first marking pulse corresponding. to the character J will cause relays R1 and R2 sequentially to close their marking contacts M. When the transmitter-distributor arm AR1 has reached the conducting segment I, marking or. negative battery will be connected to the contact I of the enciphen'ng contact apparatus CC1 over a circuit which includes the marking contact M and armature of relay R2, the inner ring RG1, the brushes BB1 and BB1, the conducting segment I of transmitter-distributor TD1 and contact I of the enciphering equipment EQ. The negative or marking potential will then be applied to point PT1,

which will cause the armature of relay R5 to close its marking contact M. This will also cause relay R6 to close its marking contact M. Thus a marking pulse will be transmitted by the radio transmitter RT to the receiving station.

The enciphering "contact equipment 001 as shown is set for the character D in which. the first and fourth pulses are marking pulses and the other three pulses spacing pulses. The marking pulse supplied by teletypewriter TTY1, when mixed with the marking pulse of the contact device 001, resulted in a marking pulse for the radio transmitter RT.

The second pulse of the character J is also a .marking pulse, as already stated, but it is observed that the contact 2 of the enciphering equipment EQ is in its spacing position, as al ready noted. In this case when the arm ARi reaches its conducting segment 2 the negative or marking battery will be connected to point P'Iz over a circuit which includes the marking battery connected to the marking contact M and armature of relay R2, the ring RG1, brushes 'BRi and BRi, conducting segment 2 oi transmitterdistributor TDl, contact 2 of the enciphering contact equipment C01 and point PT2. This will cause the armature of'relays R5 and Re to close their spacing contact S. Thus a spacing pulse will .be transmitted by the radio transmitter instead of the marking pulse prepared by the teletypewriter TTY1.

The third pulse prepared by the teletypewriter TTYI will be a spacing pulse, and thiswillfmix with a spacing. pulse at contact 3 of the enciphering contact equipment CO1. As willbe readily apparent from the description of the operation of the apparatus, a markin pulse will be trans- 'mitted as thethird pulse by the radio transmitter RT. Similarly, the fourth and fifth pulses transmitted by the radio transmitter RT will also bemarking. pulses. Thus pulses transmitted by the radio transmitter RT will correspond to the letter T X of the Baudot code. It will be understood that subsequent characters J prepared by the teletype-.

writer TTYl will ordinarily. result in the transmission of still diiferent teletypewriter charace ters, the characterstransmitted by the radio if transmitter depending upon the characters of the enciphering code with which. the teletypewriter characters are mixed.

Fig. 2 shows a radio receiver RR, together with demodulating. equipment which may be of wellknown type, for demodulatingfthe received radio signals into DC telegraph signals corresponding to the transmitted signals. The received signals as demodulated will actuate the relay R11, mov ing the armature of relay R11 between its marking and spacing contacts M and S in accordance with the marking and spacing pulses received, The designation MGn represents the receiving magnet of the reperforator-transmitter RET which'receives a starting or spacing. pulse at the i beginning of each received character, the starting pulse releasing the armature of the magnet MG11, whereupon the rotor ARn will be allowed to rotate through one complete. revolution. As is well known, each rotation of the rotor ARM of the reperforator will produce a set of five or less punched holes in a paper tape, the punched holes corresponding to the code of the character which was received by the radio receiver RR. This tape is, of course, suitable for use in retransmitting the received signals from a transmitter-distributor TDz. 1

In accordance with one of the features of this invention the reperforator-transmitter just referred to is added to the circuit ahead of the deciphering equipment DQ. This allows the re perforator to store up incoming signals in the perforated tape during the time required for resynchronizlng the deciphering equipment DQ with respect to the transmitter-distributor 'I-Dz as will be explained hereinafter. Without thereperforator any signals received during the process of resynchronization might be entirely lost. Fig. 2 shows the reperforator-transmitter RET cut away so as to illustrate the tape TP passing through a punch block PB, the punched tape then traversing the usual transmitting head TH which is rotatable about an axis AX. The transmitter-distributor TD2 of the reperforator-transmitter RET includes the usual contact device TC having five contacts controlled by an equal number of sensing pins (not shown). These contacts will assume positions corresponding to the .holes in the tape which in turn were determined by the, pulses received by the reperforator from the radio receiver RR. As soon as the radio. receiver RR has received the character X, the tape '1? will be punched and advanced one step. The punched holes in th tape TP corresponding to this character will then enter the transmitting head TH. This will then cause the second contact of the transmitter-distributor TD2 to be in its spacing position while the other contacts I, 3, 4 and 5 will be in their marking positions, as

shown.

The deciphering equipment DQ includes a contact device CC: having a series of five contacts which are positioned according to the character punched in the deciphering tape (not shown) which may or may not be of the endless type. The latter tape is identical with the tape used in the enciphering equipment referred to hereinabove in connection with Fig. l. The iive contacts of the deciphering contact equipment 003' are shown in positions corresponding to the character D of the deciphering code to explain the process of deciphering more clearly.

Referring to the transmitter-distributor TD2. whenever the switch SW is closed, the starting magnet SMz of the transmitter-distributor TD2 will be energized and remain energized thereafter as long as the tape TP includes punched holes 7 corresponding to characters to be deciphered. Energization of the starting magnet SM2 withdraws its stop-latch and releases the brush arm AR2 in the usual manner so that the brushes whereupon the armature of relay R12 will closeits spacing contact S. Relay R12 will cause relay R13 also to close its spacing contact S. Thestarting magnet SM3 will then be energized over a. circuit which includes positive battery con-. nected to the contact S of relay R13, the armature of relay R13, the ring RG3 of the deciphering equipment DQ, the brushes BRs and BR3' of the deciphering equipment DQ, the Winding of the starting magnet SM3 and negative battery which is connected to ground. As the starting magnet SM3 becomes energized, it releases its brush arm AR3 so that it may rotate through one complete revolution.

Simultaneous with the energization of the starting magnet SM3, the relay R14 will likewise be energized because its lower or main Winding is connected in parallel with the winding of the starting magnet 8M3. R14 opens its marking contact M, current which has been flowing through the lower or main winding of relay R15 from batteries B13 and B11 is in- As the armature of relay lowerv or looking winding. of relay R16 holds the.

relay inthis position until a current of opposite polarity flows in the main winding. Relay R16 in turn will cause'relay R11 to close its spacing contacts. The magnet MG: of the receiving teletypewriter TI'Y3 will then receive spacing current to start the teletypewriter printing mechanism in the-usual manner. V

If the tape 'I'Bis perforated according tothe teletypewriter character X, as was assumed hereinabove, the first pulse willbe a marking pulse and the contact No.1 of-the contact device TC2 will bein its marking position. as shown in the drawings. In that case when the brush BB2 is on the-No. 1 segment of. the transmitter-distributor TD2, negative or marking battery wilibe connected to the main or upper winding of relay R12 over a. circuit which includes contact No. 1 of the transmitter-distributor TD2, segment I of the outer ring. of the transmitter-distributor TD2, brushes BR2' and BR2, the back contact and in-. ner armature of relay G, the upper or main winding of relay R12. andground. The armature of relay R12 will-then .move to itsmarking contact M, causing relay R13 also to move its armature to its marking contact M. During the time that 'brush;BR2 is on segment I of transmitter-disdeciphering vequipmentDQ, the conducting segment! of. the deciphering equipment DQ, contact No.1; of contactdevice CO3 and point PT11. As negative batteryis applied to point PT11, the armature of relay R16 will be moved to itsmarkingcontact M.- RelayRn will follow relay R16 and move its armature also .to its contact M. The magnet MG3 of the receiving teletypewriter 'I'TYa. will also respond to. this marking pulse in the usual manner.

The punched tape TP will register aspacing pulse for. the second pulse of the received character X, as already noted. This spacing signal will cause the contact No. 2 of the distributor contact device -TC2-t o beinits spacing position as shown. Inasmuch as no battery is connected to the spacing contacts of device TC2, there will be an absence of current in the circuit to the main winding of relay R12 while the distributor brush BB2 is on segment 2. This circuit to the main winding of relay R12 includes segment No. 2 of the outer ring of the transmitter-distributor TD2, brushes BR2' and BRz, the back contact and inner armature of relay G, the main or upper winding of relay R12 and ground. Relays R12 and R13 will. therefore, move their armatures to their Spacing contact S. When the brush BR3 reaches conducting segment 2, Spacing or positive battery will be connected to point PT12 over a circuit which includes-the spacing contact S and armature of relay-R13, ;innei' -ring RG3, brushes BB3 and BB3" contact No. 2 of the contact device CC?" topoint PT12. As positive potential is appliedv to point PT12, the armature of relay R16 will remain on its marking. contact M. Relay R17 following relay R16 will alsoremain on its marking contact and the marking pulse will then be received by the magnet MGs of the teletypewriter' T'I'Ys. "Thus the second pulse received from the transmitterdistributor TD2 which is of a spacing character will be registered by the teletypewriter' 'I TYa as a marking pulse. 7 7

Similarly the tape TP signal for the third pulse of the receivedcharacter X. This marking signal will cause negative battery to be connected to the main windin of relay R12, as already explained. Relays R12 arid R13 will cause their armatur'es to close their marking contacts M. But the third contact of the deciphering contact equipment 003, being in its spacing position, will connect negative battery to the point PT12, causing the armature of relay R16 to close its spacing contact S- Relay R16 will, therefore, cause relay R17 and magnet MGaof the teletypewriter TTY3 to register a spacing signalfor the third pulse. Thus the received marking pulse will be translated into a spacing pulse by the deciphering equipment DQ. It will be obvious that the received fourth and fifth pulses of the character X, which are both of the marking type as perforated in the tape TP, will be converted tacts of the deciphering contact equipment CCs.

It will, therefore, be observed that the decipherwill register a} r'narking ing equipment DQ wil convert the received character X-which is different from the character J produced in the teletypewriter TTYI at the transmitting station into a character, namely, character J1Which is identical with that produced at the transmitting teletypewriter 'I'IYi. .Without rectly to the deciphering equipment DQ, the conversion to reproduce the original character would have required the synchronous operation of the contacts of'the code device CCaOf the deciphering equipment'DQ with respect to the similar contacts CCl of the enciphering equipment EQxatthe transmitting station (Fig. 1'). Upon inclusion of the reperforator-transmitter arrangement RET, if the radio receiver RRwere connecteddr' the reperforator-transmitter RET, the'conversion to reproduce the original character has required the synchronous operation of the contacts of. the code device 002 of the deciphering equipment DQ with respect to the perforations in the tape T? as retransmitted by the reperforator-transmi-tter RET at the receiving station. Withoutthisfsy'nchronization the characters reproduced by the teletypewriter TTYa Each character perforated: in the tape: is mixed with a different character set up in the contact device CCa'of' the deciphering equipment would be unintelligible;

The transmitter-distributor TD'2 and the deciphering"equipment will" then be desynchronized with respect to the actual signals received. In that case the reproduced signals recorded by telet'ypewriter TTYa will be unintelligible. The reproduced signals will also be unintelligible if the received signals are faded out or are otherwise attenuated or substantially suppressed. In that case the transmitter-di'stributor will also 'run out of phase with the actual signals received. Intelligibility'may be restored for characters receivedv in the tape TP after the. disturbances above-mentionedv have occurred by shifting the phase of the deciphering equipment DQ with respect to the transmitter-distributor T132.

In order to advance or retard the deciphering equipment DQ withre'spect tov the perforatedtape TP, the keys K1 and'Kz of the resynchronizing device RDzm-ay be operated. It will be shOWnherB- matter. that a single operation of ke K1 will momentarily stop the transmitter distributor T132 while the deciphering equipment DQ is allowed to proceed for one character; Similarly the key K2 may be operated once so as to hold deciphering equipment DQ inoperative while the tape TP in the transmitter-distributor TD2 will be advanced one character. Either of these keys Kl or K2 may be reoperated any desired number of times to advance one of the equipments withrespect to the other by any desired number of characters. Counters CIi and GT2 will indicate the number of timeskeys K1 and K2, respectively, have been operated.

Condenser C3 willbe charged from battery B1 when key K1 is in its idle position. Likewise condenser C4 will be charged from battery B: when key K1 is in its idle. position. Upon the operation of key K1, condenser C3 will discharge through the winding of relay E. Rela E will be operated by the dischargecurrent for a predetermined interval of time as, for example; one-third of a second. In its operated position the left armature of rela E'will open thev circuit of the starting magnet 8M2 of the transmitter-distributor TD2,

.thereby' causing the 'transmitter-distributor to stop when its rotor AR2 reaches its stop latch. The right armature of relay E will short circuit the output of the transmitter-distributor'TD2 for the time during which relay E remains operated as, for example, 0ne-third of a second, but this short circuit is of no. consequence from the standpoint of'the operation of key K1. I

' The operation of key K1 also allows the previously charged condenser C4 to discharge through the winding of the relay F, the discharge current and: theslow-release time of .the relay being 'sufiicient to maintain relay F operated for a predetermined period of time, as for example, milliseconds. While relay F is operated, condenser cs will be charged from battery B4 through aci-rcuit provided by the armature and front contact of relay F. When relay F releases, however, condenser C5 will discharge into the winding of relay G; which is also of the slow-release type.

' The circuit of relay G is designed to operate and release in a predetermined period of time as, for example, 22 milliseconds. The operation of relay G will open the circuit between the transmitter-,- distributor T132 and the deciphering equipment DQ at the back contact of the inner armature of rela G, thereb giving a desired starting pulse of the usual duration to the deciphering equipment DQ. This starting pulsein turn permits gthe magnet SMc tobecome operated to cause. the.

rotor AR: of the deciphering equipment DQ to rotate through one complete revolution.

The function of relay F is to delay transmission of the above-mentioned starting pulse to the deciphering equipment DQ until the rotors ARz and ARs of the transmitter-distributor TD2 and the deciphering equipment DQ. respectively, are brought to rest on their stop latches. The relay G times the starting pulse. The outer armature and contact of relay G control the operation of the pulse counter CT1, the counter CT1 registering each operation of key K1. This pulse counter, as well as pulse counter GT2, are of well-known types and may be returned to their starting positions in any well-known manner.

The operation of key K2 will cause condenser C6 to discharge through the winding of relay E, this discharge current being approximately of the same magnitude as the discharge current of condenser C3. The discharge current will hold relay E operated, for example, about one-third of a second. As already explained, the relay E will stop the transmitter-distributor TD2 by opening the circuit of the starting magnet SM2 at the left contact of the relay. The right armature and make contact of relay E will short circuit the transmitter-distributor 'I'D2.

The lower contact of key K2 when operated Will interrupt the flow of current through the Winding of relay H and this relay will release after a predetermined interval of time as, for example, 165 milliseconds. Upon the release of relay H, condenser Cw will discharge through the winding of relay K. Relay K is designed to be operated by the discharge current for a predetermined interval of time as, for example, 22 milliseconds. The operation of relay K will connect ground through its inner armature and make contact to the starting magnet SM2 of the transmitter-distributor TD2, allowing the transmitter-distributor T132 to be restarted. But no starting pulse'will be transmitted to the deciphering equipment DQ because the output of the transmitter-distributor TDz is short circuited by the right armature and front contact of relay E. In other words, the transnutter-distributor TD2 will be advanced one step by the operation of key K2, while the decipherin equipment DQ including its decoding contact de vice 003 will remain idle. The tape TP will thus bev allowed to advance one character step with respect to the deciphering equipment DQ. The

outer armature of relay Kwill control the regis tration by the pulse counter T2 of the operation of key K2.

It will be observed that key K1 will advance the deciphering equipment DQ by one step or charaoter with respect to the transmitter-distributor independently of the length of time during which key K1 remains operated. Similarly key K2 will be used to advance the transmitter-distributor by one step or character with respect to the deciphering equipment DQ independently of the time during which key K2 remains operated. Repeated operations of these keys will advance one equipment with respect to the other by anydesired number of steps or characters independently of the time during which the keys remain depressed. The counters 0T1 and GT2 will indicate the total number of operation of these keys as well as the difierence between these operations.

Assume that an error creeps into this receiving apparatus and that thereafter the reproduced signals of the teletypewriter TTYs becomes unintelligible, Such unintelligibility is usually due to the deciphering equipment DQ being out of step with 10 the characters as perforated in the tape TP. When this happens, the attendant will operate key K1 once and observe the teletypewriter TTYs to determine whether unintelligibility has been restored to the reproduced signals or characters. If the unintelligibility has not been restored with one operation of key K1, the attendant will operate key K1 one or more additional times and again observe Whether or not intelligible signals appear at the receiving teletypewriter TTY3. If intelligibility is not restored by those operations of key K1, the attendant will then quickly .operate key K2 the same number of times as he has previously operated key K1, and furthermore he will operate key K2 one or more additional times. Intelligibility may then be restored to the signals or characters at teletypewriter TTYa. The keys K1 and K2 provide the attendant with a ready means for effectively shifting the decoding contact device CCs of the deciphering equipment DQ forward or backward with respect to the tape TP of reperforator-transmitter RET, and the number of characters shifted and the direction of the shift will be indicated by the readings of the counters GT1 and GT2.

As soon as the teletypewriter TTY2 reproduces intelligible text, t e tape TP and the coded tape (not shown) which controls the contact device CCs of the deciphering equipment DQ may both be set back the same number of characters in a wellknown manner to a region of the tape where the error occurred, or even to some region beyond that point. The switch SW may then be operated to restart the apparatus for a re-run to record on the teletypewriter T'IYs the text which was lost in the first instance. During this time, however, further characters may be received by the radio receiver RR, and these characters will be recorded by the perforated tape TP of the reperforator of Fig. 2 to .be reproduced thereafter. To hasten the reproduction and recording of these additional characters it may be desirable to increase the speed of the transmitter-distributor 'ID2, the deciphering equipment DQ and the teletypewriter TTY3 at the receiving station from. for example, 60 speed operation to '75 speed operation. By so doing the time lost in the resynchronization process may be overcome in a relatively short time. Any error that appear in the text reproduced by the teletypewriter TTYs will then be only those due to the receipt of voltages by the radio circuit or other transmission channel which obliterate the transmitted signals or characters, and will not be due to any absence of synchronism between the ciphering and deciphering devices.

The method of re-setting the two tapes at the receivermay be as follows: Whenever copy becomes unintelligible at teletypewriter 'IIYa, the reperforator-transmitter RET may be stopped by opening switch SW, if so desired. Marks may be inscribed by pencil or otherwise on the tape TP and on the deciphering tape (not shown) at points the same number of characters back along both punched tapes after they have passed the sensing pins. In other words, the reference marks will designate points on the tapes corresponding to characters already deciphered. These characters may be those in the textiprior to loss of intelligibility due to lack of synchronism. Then the key-controlled resynchronizing device RD will be manipulated as already described to restore intelligibility to the text. Then the tape TP is set back in any well-known manner to place its reference mark at its sensing pins.

The difference between the readings. of counters GT1 and GT2 will determinethe number of characters by which the deciphering tape reference mark should be shifted forwarder backward from its sensing pins. The relative positions of the two tapes now are such as to provide intelligible copy of the signals or characters previously lost due to lack of synchronism.

The transmitting head TD of the transmitterdistributor TDz will be in the position shown in the drawings as long as there is suflicient tape TP interposed between the punch block PB and the transmitting head TH. As the tape TP becomes taut, the transmitting head TH is rotated about its axis AX in a counter-clockwise direction toward the punch block PB by the tape feed mechanism (not shown) and registers at the contacts of the transmitter-distributor TD2 the signals conveyed by the tape perforations. The transmitting head TH will continue to rotate in a counter-clockwise direction through an increased angle until it reaches the punch block PB. Then the contacts ON on the transmitting head TH will open the circuit of the starting magnet 8M2 to stop the operation of the transmitter-distributor TDz. This form of teletypewriter operation which involves a creeping up the tape transmitter is well known and need not be further described. I I

Although the enciphering equipment EQ'at the radio transmitter of Fig. l and the deciphering equipment DQ at the radio receiver includecontact devices CC1 and C03, respectively, both of which have been described as operated or controlled by tapes (not shown), it will be understood that the contact devices CO1 and CO3 may be operated or controlled by other well-known apparatus which does not employ tape. For example, the contact devices G1 and CC3 may be operated or controlled by a plurality of cams of different formations so as to assign different positions to the contacts of these contact devices CO1 and CCs from character tocharacter. In using tapes or cams or other apparatus for the enciphering and deciphering functions, it is essential'that the tapes or cams, etc., provide a plurality of different characters arranged in a predetermined order and that these characters be arranged in the same order at both stations.

The receiving system of this invention may be used for the decipherment of ordinary telegraph signals of the Morse type, for example. Such received signals would be typed manually on a teletypewriter having a perforator (otherwise known as a keyboard perforator) and the perforated tape then'inserted in the transmitterdistributor 'IDz. The received signals will then be decipheredin the manner described above, the proper deciphering tape being used in the deciphering equipment DQ for the deciphering process. Any required resynchronization to restore intelligibility to the signals recorded by the teletypewriter T'IYs would be performed by the key-controlled equipment RD.

The resynchronizing apparatus RD is described for illustrative purposes as including slow-release relays. It will be understood that other timing devices or circuits, including condensers and resisters, etc. of well-known form may be substituted therefor within the scope of this invention.

The time and other constants given hereinabove for illustrative purposes are not to be construed as limitations'upon the invention. The apparatus of this invention may be caused to operate satisfactorily with time constants of widely different magnitudes.

Although the invention has been described as applied to a secrecy system in which but one tape or equivalent device is employed for the enciphering process and an identical tape or equivalent device for the deciphering process, it will be understood that two or more such tapes or other devices may be used whenever desired. Such tapes or devices may be applied to the signals or characters simultaneously or in tandem in any well-known manner.

Although the invention has been described as applied to a radio system for transmitting teletypewriter signals between two stations, the invention is equally pplicable to wire circuits, etc. It will also he understood that the apparatus has been described for the one-way transmission of teletypewriter signals merely for illustrative purposes; the circuits may be modified by those skilled in the art for the two-way transmission of signals. The signals need not be of the Baudot type but may be any form of telegraph signals well known in the art.

While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and Widely Varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a teletypewriter secrecy system, the combination of means for perforating a first tape in accordance with received signals, deciphering means including a second tape perforated according to a deciphering code, said means being responsive to the perforations of both tapes to reproduce the original signals from the received signals, said means including means to advance one of the tapes with respect to the other when said tapes become de-synchronized to restore intelligibility to said signals as reproduced.

2. In a teletypewriter secrecy system for reproducing original signals from the signals received by the system, comprising means for perforating the tape in accordance with the received signals, a transmitter-distributor controlled by said perforated'tape, deciphering equipment con= nected to said transmitter-distributor and including a tape perforated according to a predetermined deciphering code to control the deciphering equipment, a teletypewriter connected to the deciphering equipment for recording the sig nals reproduced thereby, and means for advancing the deciphering equipment with respect to the transmitter-distributor by any desired amount in order to synchronize the deciphering equipment with the tape perforations controlling the transmitter-distributor.

3. Ina teletypewriter secrecy system, the combination of means for providing a first tape perforated according to received signals, a second tape perforated according to a deciphering code, means controlled by both tapes for mixing the signals perforated in said tapes synchronously, and key-controlled means for advancing one of the tapes with respect to the other by any predetermined amount to re-synchronize the two tapes whenever they become de-synchronized.

4. In a teletypewriter secrecy system, the combination of means for perforating a first tape in accordance with received signals, a second tape.

perforated in accordance with a predetermined deciphering code, means controlled by both tapes for deriving the original signals from the received signals, said means including a key-operated device for advancing one of the tapes with respect to the other by a predetermined interval to synchronize the two tapes.

5. In a teletypewriter secrecy system, the combination of a reperforator for perforating tape in accordance with received teletypewriter signals to provide a loop of perforated tape, a transmitter-distributor controlled by said perforated tape, deciphering equipment connected to said transmitter-distributor, said deciphering equipment including a second. tape perforated in accordance with a predetermined deciphering code and controlling said deciphering equipment, and key-controlled means for advancing one of the tapes with respect to the other by a predetermined number of characters when said tapes are out of step, thereby rendering the reproduced signals intelligible whenever the reproduced signals become unintelligible.

6. In a teletypewriter secrecy system in which teletypewriter characters are transmit-ted over a medium which may introduce extraneous voltages or the like into the transmission of said teletypewriter characters to render the reproduced characters unintelligible, comprising means for producing a first tape perforated in accordance with the received characters after transmission through said medium, a transmitter-distributor controlled by said perforated tape, deciphering equipment including a second tape perforated in accordance with a predetermined deciphering code, and means for synchronizing the two tapes comprising a key-controlled device for advancing one of the tapes with respect to the other by a predetermined number of characters.

'7. In a telegraph secrecy system, the combination of means for converting intelligible signals into unintelligible signals for transmission to a distant point, said means including a device having a code of enciphering signals to be mixed with said intelligible signals to render said intelligible signals unintelligible, means for reconverting said unintelligible signals into their original intelligible form, said latter means including a device having a code of deciphering signals which is identical with the code of enciphering signals, and key-controlled means for changing the phase of the deciphering signals with respect to the enciphering signals by any desired amount.

8. In a teletypewriter secrecy system, the combination of means for converting teletypewriter characters into other teletypewriter characters for transmission to a distant point in unintelligible message form, said converting means including means for enciphering said characters with a predetermined code of teletypewriter characters, means for reconverting said transmitted teletypewriter characters into their original intelligible form, said latter means including means for deciphering said characters according to a predetermined code which is identical with said enciphering code, and means for advancing the deciphering code with respect to the received characters by any desired amount,

9. A teletypewriter secrecy system comprising a perforator for perforating tape in accordance with received signals, a transmitter-distributor controlled by said perforated tape, a loop of said perforated tape being provided between said perforator and said transmittendistributor, deciphering equipment connected to said transmitterdistributor, said deciphering equipment having a 14 tape perforated according to a predetermined code which is intended to be stepped synchronously with respect to the first-mentioned perforated tape, extraneous effects being introduced into the perforator to de-synchronize said tapes, and means for changing the relative positions of said tapes for restoring synchronism between said tapes.

10. Ateletypewriter secrecy system comprising a perforator for perforating tape in accordance with received signals, a transmitter-distributor controlled by said perforated tape, a loop of said perforated tape being provided between said perforator and said transmitter-distributor, deciphering equipment connected to said transmitter-distributor, said deciphering equipment having a tape perforated according to a predetermined code which is intended to be stepped synchronously with respect to the first-mentioned perforated tape, extraneous effects being introduced into the perforator to de-synchronize said tapes, and means for restoring synchronism between said tapes, said latter means including means to start said transmitter-distributor one or more times while maintaining said deciphering equipment stationary.

11. A teletypewriter secrecy system comprising a perforator for perforating tape in accordance with received signals, a transmitter-distributor controlled by said perforated tape, a loop of said perforated tape being provided between said perforator and said transmitter-distributor, deciphering equipment connected to said transmitter-distributor, said deciphering equipment ment having a tape perforated according to a predetermined code which is intended to be stepped synchronously with respect to the firstmentioned perforated tape, extraneous effects.

being introduced into the perforator to de-synchronize said tapes, and. means for restoring synchronism between said tapes, said latter means including means to start said deciphering equipment one or more times while maintaining said transmitter-distributor stationary.

12. A teletypewriter secrecy system comprising a perforator for perforating tape in accordance with received signals, a transmitter-distributor controlled by said perforated tape, a loop of said perforated tape being provided between said perforator and said transmitter-distributor for storing the received signals, deciphering equipment connected to said transmitter-distributor, said deciphering equipment having a tape perforated according to a predetermined code which is intended to he stepped synchronously with respect to the first-mentioned perforated tape, extraneous effects being introduced into the perforator to desynchronize said tapes, and means for restoring synchronism between said tapes, said latter means including means to step the transmitter-distributor ahead or behind the decipher ing equipment by one or more steps, and means for indicating the number of steps by which the transmitter-distributor leads or lags behind the deciphering equipment.

13. In a teletypewriter secrecy system, the combination of a first device having a plurality of contacts controlled by received teletypewriter characters, a second device having a plurality of contacts controlled according to a deciphering code, said contact devices being operated stepby-step in synchronism, said devices becoming desynchronized during abnormal conditions of reception of said teletypewriter characters so that the deciphered characters become unintelligible,-

received telegraph signals according to a predetermined code identical with the code employed for enciphering the telegraph signals before transmission, extraneous efiects being introduced into said reconverting means to dc-synchronize the received telegraph signals With respect to the re-converting means, and key-controlled means to change the relative position of the received telegraph signals with respect to the deciphering device of said reconverting means to restore synchronism between the received telegraph signals and the re-converting means.

EDWIN WALTER BEMIS. 

